Hole saws in thick steel

[Memmeddu]

Best advice. Don't!
I needed 3x 35mm holes in 12mm steel plate. My rotobroach cutters are 38mm unfortunately. I bought a Starrert hss hole saw with 8% cobalt. Ran it slowly in the Bridgeport. About 200rpm. Used flood coolant. Started well but soon stopped cutting. No chip clearance so needs constant blowing out. After 1 hole it was knackered. Off to Screwfix and bought a Bosch hss cobalt. No arbor with pilot drill. £25 extra . I didn't bother. Held it in an ER32 collet fine. Pilot drill not necessary either.
After 1 hole it also died
@DAPPH said he could fix it. I was rather dubious but fair play 2 minutes with a triangular file and it was as good as new again!
Rotobroach always from now on!

You did something wrong
I've cut 24 consecutive holes on 10mm thick pillars bases (welded in wrong position) using a cheap parkside HSS hole saw and my mag drill.
Yes you have to constantly relieve the cut to break the chips but till you're doing that you'll be fine.
And I've been surprised by the accuracy of the hole, the first 2mm were off because the slack in the dovetails but I've eventually used a piece of 25mm ground induction hardened bar and it fitted snug in the holes.
I didn't use coolant but cutting oil because it sticks better on the tool .

 

[Morris]

If you are cutting either the hole or slug to waste - and they don't need to be perfect, then drill a couple of swarf clearance holes to intersect the cut line, either just inside, outside or on directly on the middle.

It will greatly improve the cut speed and longevity of the saw. It is swarf clearance that is the problem with holesaws, it packs the cut up and causes the saw to overheat, and then they are done. The only other way is to peck drill and clear the cut often.

This as well.

 

[oldbikedavey]

I would respectfully suggest it is not such a good idea. Unless the two sides of the piece being cut are straight and parallel, it will overconstrain the piece and not help. If we look at a table saw for wood, they do not have a double fence for the same reason. An important principle in cutting is to use one and only one reference edge.

Could use sprung rollers or something like that, maybe ball transfer units ?
Using a shaper gauge to set things up would be a step towards better parallelism, I think.

 

[Agroshield]

Could use sprung rollers or something like that...

Traditionally in woodworking, that is called a featherboard. Its primary purpose is to push the reference edge of the material into intimate contact with the reference edge of the machine (the fence). In other words, it is there to strengthen/increase/assure the 'use one and only one reference' principle.

If it is sprung-loaded, there is no requirement for it to be parallel to anything. If you look at a featherboard, its fingers are angled, both to provide the 'spring' and also give some useful protection against kickback. There is some logic to say that more pressure can be applied further from the blade (high pressure near the blade can cause the kerf in the stock on the exit side of the blade to close up), hence parallelism might in reality be a disbenefit.

 

[fizzy]

I would respectfully suggest it is not such a good idea. Unless the two sides of the piece being cut are straight and parallel, it will overconstrain the piece and not help. If we look at a table saw for wood, they do not have a double fence for the same reason. An important principle in cutting is to use one and only one reference edge.

I thought so as well but the proof of the pudding is in the eating as they say.
It was quite a long cut. I tried the plate both ends to make sure it was moving ok.
An accuracy of about a thou along the whole length can't be bad!

 

[fizzy]

Thats my take on it BS, the bigger they are the more pressure needed. Like any big drill, go to lightly and you will rub off the cutting edge. @fizzy I now have BIC ( bandsaw inferiority complex)

Bob

Well I thought my 24" Startrite was huge - until I acquired this one
Not used it on metal yet - has a very coarse ripper blade for wood. Variable speed on the fly like a Bridgeport and a table rack feed. 36" throat!

 

[brightspark]

I find doing larger holes in steel using a HSS holesaw if you put one or two 6mm holes near the edge your cutting it helps remove the chips and of course plenty of cutting fluid, that’s if you don’t want the centre blank obviously

paste is a lot better than fluid on hole saws i generaly give all my hacksaw blades and hss drills a dab of it . cuts faster reduces friction and your gear lasts a lot longer

 

[Scruffywelder]

I've taken an el cheapo 6" holesaw through 1" steel plate (of unknown provenance) before now.

Dads old (wartime) J&S pillar drill has a bottom speed of about 36rpm with the backgear in due to being converted to a reduction-geared motor. Half a dozen 1/2" holes round the periphery to let the swarf drop through and turning the workpiece over about halfway and cutting from the other side helped.

Smaller ones I've rigged a low-ish pressure blowgun up from the compressor to clear the cut out and just pecked it steadily.

Bit slow but it can be done...

 

[bricol]

I've put a 5" hole saw through 10mm 304 stainless in a pit in a Fort Worth, Texas in 2002/3, using a Dewalt cordless drill - the switch was knackered after doing that. Slow, clearing the cut, and lots of Rocol cutting lubricant - I still have the hole saw, it still cuts.

Lubricant, not coolant, slow (not 200rpm) and accepting you need to clear the cut, and they work fine, and last. It's a hole saw, not a machining cutter like a rotabroach.

A new switch in the drill (from Granger in Northridge, LA - where the next job was) and the drill was fine in case you were wondering - the continuous on and off for the time required didn't do the contacts any good.

 

[Erie Fred]

I thought you was buying a plasma cutter ?

 

[fizzy]

I've put a 5" hole saw through 10mm 304 stainless in a pit in a Fort Worth, Texas in 2002/3, using a Dewalt cordless drill - the switch was knackered after doing that. Slow, clearing the cut, and lots of Rocol cutting lubricant - I still have the hole saw, it still cuts.

Lubricant, not coolant, slow (not 200rpm) and accepting you need to clear the cut, and they work fine, and last. It's a hole saw, not a machining cutter like a rotabroach.

A new switch in the drill (from Granger in Northridge, LA - where the next job was) and the drill was fine in case you were wondering - the continuous on and off for the time required didn't do the contacts any good.

Low gear on a battery drill is higher than 200rpm I suspect.
I used 10% coolant mix instead of the usual 5%. Always worked fine before.
Maybe this plate is hardox or something else exotic.

 

[fizzy]

I thought you was buying a plasma cutter ?

I have a plasma cutter. I have built a cnc one just not had time to finish it. If I had known how long these holes would take I would have put the effort into the plasma instead

 

[Tigman]

You can buy 35mm cutter for mag drill !

 

[Morrisman]

plenty of paste and doing it in a pillar or hand drill drill works well as you can back it off quick for swarf clearance

I do it like that, but have my shop vac held to the side, so it sucks up the swarf of the cutter every time you back out of the groove.
I use spray on cutting lube directly into the groove. Not quick, but it gets the job done.
And hole saws never cut to size, until the time you actually want one to…

 

[fizzy]

You can buy 35mm cutter for mag drill !

You can indeed. Bit they aren't cheap and wanted to finish this weekend and nothing available in time. Broach cutters are vastly superior.

 

[sako243]

Oh I'm going to be in for some fun then. Got two 50mm holes to drill through 10mm plate welded to 3mm thick 40mm depth box... Hopefully close but far enough to miss the 20mm bracket on the back

Doesn't need to be precise as just to weld in a bush so if my plasma was behaving I might have used that

 

[fizzy]

Oh I'm going to be in for some fun then. Got two 50mm holes to drill through 10mm plate welded to 3mm thick 40mm depth box... Hopefully close but far enough to miss the 20mm bracket on the back

Doesn't need to be precise as just to weld in a bush so if my plasma was behaving I might have used that

My plasma is fine but not got the cnc running properly yet. You are welcome to.pop over and use it free hand. I also have a hole compass for it but 50mm might be too small.
Hope to have cnc running in a week or 2.

 

[Erie Fred]

I have a plasma cutter. I have built a cnc one just not had time to finish it. If I had known how long these holes would take I would have put the effort into the plasma instead

I meant the straight line sawing job.

 

[fizzy]

I meant the straight line sawing job.

Ahh.
I am useless at anything freehand. Even using a straight edge my plasma cutting is a mess. My bandsaw gives an awesome finish and amazing accuracy. Love a chance to use it properly instead of just cutting firewood!

 

[sako243]

My plasma is fine but not got the cnc running properly yet. You are welcome to.pop over and use it free hand. I also have a hole compass for it but 50mm might be too small.
Hope to have cnc running in a week or 2.

Suitably bodged . Well there's no point doing a decent job on what was a bodge job to begin with.

Tried the hole saw but because I wanted to keep it close to the 20mm bracket so I could use it as a gusset the cheapo teeth bent over on the fillet weld so it's now useless (well a whole set from about 1/2" to 5" was £20 bought to do one hole in a floorboard so it's on its bonus life now).

Surprisingly my plasma decided it was going to play ball today so I managed to cut / gouge out most of the hole (couldn't get into the corners easily) and then the wee M12 die grinder came into its own - that thing is a beast considering it's size. Anyway some filling of holes with weld and we have one of the bale spikes mounted.

The forks are all twisted and bent from abuse (I'm surprised they have lasted 4 years with the abuse I've given them). You saw the silly 10ft extensions I have for them. For the cost of two bushes when I eventually kill these I'll get some proper ones made up but I suspect I'll just keep using, abusing and repairing these lashed up at 3am in 1.5h with a misbehaving welder, plasma cutter and little sleep.